1. Field of the Invention
The present invention relates generally to an antenna device, and more particularly, to a compact antenna device suitable for installment in a portable terminal and tunable to a resonant frequency.
2. Description of the Related Art
Portable devices such as notebooks and portable terminals require compact antennas in order to receive television (TV) signals and other signals. In this case, antennas having meandering or helical shapes may be considered as compact high performance antennas. However, since conventional helical antennas or monopole antennas are compact, they provide narrow bands and are difficult to match with portable terminals.
European Patent No. EP1,176,663A1 discloses a helical antenna technique used in a portable terminal. In the disclosure, a terminal is installed in an intermediate or front part of an element of a helical antenna. A filter including strip lines having different lengths, an inductor, and a capacitor are connected to the terminal using a switch.
However, a helical antenna circuit is complicated, and it is difficult to minutely tune to a resonant frequency. Accordingly, there exists a need for further development of the circuitry.